freshwater eel

Freshwater eels are slender, elongated, and usually scaleless fish that spend most of their lives in freshwater but migrate to the sea to breed. They are active predators with small, embedded scales. After growing to maturity in freshwater, they return to the sea to spawn and die. The young, transparent eels drift to the coast and make their way upstream. These eels are considered valuable food fish and can range significantly in size.1

A well-known example is the European eel (Anguilla anguilla), which spawns in the Sargasso Sea. The transparent young, called leptocephali, are carried by the Gulf Stream to continental shelves, where they transform into elvers and then glass eels. They migrate upstream into freshwater, growing into yellow eels. After 10-15 years, they become silver eels and migrate back to the sea to spawn.2

It is important to note that electric eels, despite their name, are not true eels but are South American knifefishes known for producing powerful electric shocks. Swamp eels are also unrelated to true eels and inhabit tropical freshwater and brackish waters.34